The present invention relates to a method for operating an internal combustion engine of a motor vehicle, in which fuel is injected directly into a combustion chamber and burned during an intake phase in a first mode of operation and during a compression phase in a second mode of operation, and in which exhaust gas formed by combustion is sent to a catalytic converter. The present invention also relates to a controller for an internal combustion engine of a motor vehicle and to an internal combustion engine for a motor vehicle.
Such a method, such a controller and such an internal combustion engine are conventional in direct gasoline injection, for example, where fuel is injected into the combustion chamber of the internal combustion engine during the intake phase in homogenous operation or during the compression phase in stratified charge operation. Homogeneous operation is provided for full-load operation of the internal combustion engine, while stratified charge operation is suitable for idling and partial load operation. Such a direct injection internal combustion engine is switched between these modes of operation as a function of the required torque, for example. For implementation of stratified charge operation it is necessary to have a catalytic converter with which the nitrogen oxides formed may be stored temporarily in a storage catalytic converter so that they may be reduced during a subsequent homogeneous operation. The storage catalytic converter is loaded with nitrogen oxides in stratified charge operation and is unloaded again in homogeneous operation. This loading and unloading as well as the associated conversion of nitrogen oxides to nitrogen and oxygen result in aging of the catalytic converter.
It is an object of the present invention to create a method of operating a storage catalytic converter of an internal combustion engine with which the aging of the storage catalytic converter is detectable.
The exhaust gas generated in the internal combustion engine contains pollutants which are converted in the catalytic converter. These include unburned hydrocarbons and carbon monoxide. Conversion of these pollutants results in an increase in temperature of the resulting exhaust gases. However, this increase in temperature is less in the case of an aged catalytic converter due to its reduced conversion capacity. It is thus fundamentally possible to use the resulting increase in temperature as a measure of the aging of the catalytic converter.
This temperature increase occurs even without the additionally injected fuel. In this case, however, the temperature increase is so slight, e.g., in the case of an aged catalytic converter, that it may no longer allow reliable determination of aging of the catalytic converter.
An additional conversion and thus also an additional increase in temperature of the exhaust gas is achieved by injection of additional fuel. This may allow a reliable and certain determination of the aging status of the catalytic converter. In an example embodiment of the present invention, a temperature increase is measured and compared with a temperature increase measured with a new catalytic converter, and the difference is compared with an upper limit value. It is thus readily possible to detect an aged catalytic converter.
In a similar manner, a temperature increase is measured and compared with a modeled temperature increase, and the difference is compared with an upper limit value.
In another example embodiment of the present invention, a maximum temperature is measured and compared with a lower threshold value. This is an option for implementation of the present invention that may be executed especially easily and rapidly.
It may be advantageous if the additional fuel injected is not ignited. This guarantees that the unburned fuel in the form of unburned hydrocarbons and carbon monoxide will enter the exhaust pipe and the catalytic converter and result in an elevated temperature there.
Implementation of the method according to the present invention in the form of a control element which is provided for a controller of an internal combustion engine in a motor vehicle is especially important. A program capable of running on a computer, e.g., on a microprocessor, and suitable for execution of the method according to the present invention is stored on this control element. Thus in this case, the present invention is implemented by a program stored on this control element, so that this control element equipped with the program constitutes the present invention in the same manner as the method for whose execution the program is suitable. An electric memory medium such as a read-only memory or a flash memory may be used as the control element.
Additional features, possible applications and advantages of the present invention are derived from the following description of example embodiments of the present invention which are illustrated in the figures in the drawing. All the features illustrated or described here, either alone or in any desired combination, constitute the object of the present invention, regardless of how they are combined in the patent claims or their reference back to preceding claims and independently of how they are formulated in the description or illustrated in the drawing.